JP4603128B2 - Cupric chloride / sodium chlorate etching system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a management system for a cupric chloride / sodium chlorate etching solution, and a method for managing the etching solution when regenerating cuprous produced by etching copper with cupric chloride with sodium chlorate and hydrochloric acid. And apparatus.
[0002]
[Prior art]
Conventionally, methods using a ferric chloride etching reaction and a cupric chloride etching reaction are mainly used for forming a printed circuit or the like by an etching technique. The cupric chloride method is widely used because it can be kept in a new solution by regenerating with hydrogen peroxide and is easy to manage, but there is room for improvement in terms of etching factors, etc. It is left.
[0003]
In recent years, a method using sodium chlorate (NaClO ₃ ) to regenerate cuprous chloride etchant has been proposed, and has attracted attention because of its good etching factor and large liquid specific gravity, which makes it easy to recover. Yes. However, the cupric chloride / sodium chlorate etching solution (hereinafter referred to as chlorate etchant) has not been fully elucidated in its properties and behavior as an etching solution, and practical liquid management means are not specifically known. Various control methods have been known for the control items such as pH, hydrochloric acid concentration, sodium chlorate concentration, first, and copper dichloride concentration themselves, but these are the accuracy and measurement for actual chlorate etchants. It is not always accurate in terms of time. In addition, with respect to chlorate etchant, extremely dangerous chlorine dioxide and chlorine gas may be generated during the operation, and therefore, strict management in real time is necessary particularly for pH.
[0004]
An object of the present invention is to provide a liquid management method capable of comprehensively managing the above items with respect to a chlorate etchant management method and an apparatus capable of implementing this method with a relatively simple configuration.
[0005]
[Means for Solving the Problems]
The subject of the present invention is that cuprous chloride produced by copper etching with a cupric chloride / sodium chlorate etching solution is expressed by the formula: 6CuCl + NaClO ₃ + 6HCl → 6CuCl ₂ + NaCl using sodium chlorate and hydrochloric acid. When regenerating by + 3H ₂ O reaction, the pH value, ORP value, sodium chlorate concentration, and specific gravity of the etching solution are measured by corresponding sensors, and the etching solution is measured based on the signal output from the sensor. And controlling the etching solution to have a pH of 0.5 to 2.5, an ORP value of +500 mV to +1200 mV, a sodium chlorate concentration of 0 to 1 mol, and a specific gravity of 1.25 to 1.45. It is accomplished by the management method of cupric chloride, sodium chlorate based etching solution and performing.
[0006]
The management method of the cupric chloride / sodium chlorate etching solution is cuprous chloride produced by copper etching with the cupric chloride / sodium chlorate etching solution using sodium chlorate and hydrochloric acid.
6CuCl + NaClO ₃ + 6HCl → 6CuCl ₂ + NaCl + 3H ₂ O
In order to regenerate by the reaction, an etching station measurement cell having a pH sensor, an ORP sensor, a specific gravity sensor and a temperature sensor, and a replenishment signal is generated according to the processing unit and processing result of the output signal from each sensor. It can be implemented by a cupric chloride / sodium chlorate etching liquid management device characterized by having a control device provided with a replenishment instruction section.
[0007]
-Conventional etching method-As described above, the ferric chloride solution and the cupric chloride solution are mainly used in the copper etching method.
[0008]
-Ferric chloride etching reaction-Copper etching reaction with ferric chloride etching solution is as follows.
2FeCl ₃ + Cu → 2FeCl ₂ + CuCl ₂
2Fe ³⁺ + Cu ⁰ → 2Fe ²⁺ + Cu ²⁺ (ion formula)
[0009]
By etching, for example, a copper foil provided on the substrate is oxidized with Fe ³⁺ to become Cu ⁺ and further oxidized with Fe ³⁺ in the vicinity to become Cu ²⁺ and dissolved in the etching solution. Fe ³⁺ oxidized copper foil becomes Fe ²⁺ . As a result of the etching, Cu ²⁺ in the solution, Fe ²⁺ occurs, although Cu ²⁺ has an etching of the copper foil, Fe ²⁺ has no etching ability of the copper foil. The copper foil etching reaction with ferric chloride does not require supply of chlorine ions from the outside, etching is performed at a relatively high pH, and the generated Fe ²⁺ is oxidized by oxygen in the air.
4FeCl ₂ + O ₂ + 4HCl → 4FeCl ₃ + 2H ₂ O
[0010]
In this reaction, hydrochloric acid is consumed, the pH rises, and iron hydroxide sludge is generated. For this reason, an acid containing hydrochloric acid (hydrochloric acid) is required mainly for the purpose of preventing pH increase, and therefore etching is performed in a state where hydrochloric acid is present to some extent (0.2 to 1%).
[0011]
-Cupric chloride etching reaction-Cupric chloride etching proceeds according to the following reaction formula.
CuCl ₂ + Cu → 2CuCl
Cu ²⁺ + Cu ⁰ → 2Cu ⁺ (Ion type)
[0012]
That is, the copper foil on the substrate is oxidized by Cu ²⁺ to become Cu ⁺ , and is dissolved in the liquid as a cuprous complex salt by a large amount of chlorine ions in the vicinity. The resulting Cu ⁺ has no copper etching, but this Cu ⁺ can be easily regenerated to Cu ²⁺ with an oxidizing agent. In general, hydrogen peroxide is used as an oxidizing agent, and oxidation from cuprous to cupric is performed as follows.
2CuCl + H ₂ O ₂ + 2HCl → 2CuCl ₂ + 2H ₂ O
[0013]
As shown in the above reaction formula, the oxidation of Cu ⁺ with hydrogen peroxide requires hydrochloric acid. If regeneration is performed without supplementing hydrochloric acid, the pH of the etching solution increases, and the oxidation reaction of hydrogen peroxide to Cu ⁺ It does not hold, and the added hydrogen peroxide causes self-decomposition at the moment of touching Cu ⁺ . Therefore, regeneration with hydrogen peroxide ensures a sufficient amount of chlorine ions and a low pH by increasing the hydrochloric acid concentration to 2 to 4 mol. If hydrogen peroxide enters excessively into the etching solution, hydrogen peroxide undergoes self-decomposition.
[0014]
-Regeneration reaction in chlorate etchant-Etching reaction with cupric chloride / sodium chlorate etching solution itself is expressed by the above reaction formula with cupric chloride etching solution. Cu ⁺ produced in this step is a sodium chlorate solution. By adding, it is regenerated by the following reaction.
6CuCl + NaClO ₃ + 6HCl → 6CuCl ₂ + NaCl + 3H ₂ O
[0015]
This reaction requires hydrochloric acid (chlorine ions) as well as regeneration with hydrogen peroxide. Regeneration with hydrogen peroxide produces water as a by-product, but chlorate etchant produces sodium chloride (salt). In the recycling management of cupric chloride / sodium chlorate etching solution, a solution with high hydrochloric acid concentration (pH of about 0.5 or less or hydrochloric acid of 2 to 3M) without Cu ⁺ (reducing agent). When sodium chlorate is added to (cupric etchant), sodium chlorate reacts directly with hydrochloric acid to generate dangerous chlorine dioxide (Chlorine Dioxide) and chlorine gas (Chlorine gas).
2NaClO ₃ + 4HCl → 2ClO ₂ + Cl ₂ + 2NaCl + 2H ₂ O
[0016]
Chlorine dioxide is readily soluble in water, but most of it is released as a gas under process conditions with an actual cupric chloride / sodium chlorate etching solution. The relative vapor density of chlorine dioxide gas and chlorine gas is 2.3 and 2.5 respectively, which is heavier than air, and unlike hydrogen peroxide, it may directly affect human life, so strict and prompt management is required. .
[0017]
-PH control-Hydrochloric acid is necessary for the regeneration reaction as described above and causes generation of chlorine dioxide and chlorine gas. That is, when the pH is high, the regeneration reaction does not proceed, and when the pH is low, chlorine dioxide and chlorine gas are generated. That is, when a regeneration reaction occurs in a state where the hydrochloric acid concentration is very low, the hydrochloric acid is consumed rapidly and the pH immediately rises. At about pH 3 or more, copper hydroxide is generated and etching cannot be performed. On the other hand, if the pH value is 1.3 or less, chlorine dioxide may be generated by the reaction of NaOCl ₃ and HCl as described above. Thus, pH is the most important management item in the chlorate etchant. Therefore, accurate pH control (hydrochloric acid concentration control) in real time is necessary, and an appropriate pH value is in the range of 1.3 to 1.5.
[0018]
In etching with chlorate etchant, Cu ⁺ generated by etching is oxidized to Cu ²⁺ by sodium chlorate as an oxidizing agent in the same way as hydrogen peroxide in the case of conventional cupric chloride etching. There are a method of replenishing sodium chlorate in an amount necessary for the above (equivalent management method) and a method of etching always in the presence of a constant excess of sodium chlorate (excess management method).
[0019]
The former is none other than the conventionally proposed cupric chloride / sodium chloride (potassium chloride) etching solution. Even in this case, if the pH is kept high (the hydrochloric acid concentration is low), a high specific gravity (dissolves a large amount of copper). A) is obtained.
[0020]
In the latter, it is possible to strip the Cu ⁺ that remains in the copper foil surface produced by the etching in chlorate etchant, which strip the Cu ⁺ which remains on the copper surface with ferric etching chloride Fe ³⁺ of Is the same. Only when the chlorate etchant is excessively added to some extent, the characteristics of this solution are exhibited. The difference is that Fe ³⁺ becomes Fe ²⁺ when stripped by ferric chloride etching and salt is formed when stripped by chlorate etchant etching.
[0021]
-Control of cuprous chloride / cupric chloride concentration-In general, the concentration of cupric chloride / cupric chloride in the etching solution is measured by an optical concentration method or by an oxidation / reduction electrode using an ORP meter. Etc. are considered. Fig. 1 shows the spectrum of the chlorate etchant.
[0022]
FIG. 1 is a spectrum of a 1100-200 nm wavelength (infrared light to ultraviolet light) of a chlorate etchant of cupric chloride 3M and hydrochloric acid 0.1M. There is a valley that passes light well around 520 nm, and it appears to be green. In ordinary measurements (when a 5-50W lamp is used as the light source), absorption at about 400 nm or less and about 700 nm or more is saturated, and spectral changes cannot be seen. You will see changes. When Cu ⁺ is formed, this valley becomes shallower, absorption near 520 nm increases, and the liquid becomes dark. Although the Cu ⁺ concentration can be measured based on this phenomenon, information on the Cu ²⁺ concentration, hydrochloric acid concentration, and ClO ₃ concentration cannot be obtained at all.
[0023]
The measured spectrum is shown in FIG. 2 with the light source made 1000 times stronger than in the case of FIG. When a powerful light source is used, a peak is observed at about 830 nm in addition to the 520 nm valley. This is the absorption of Cu ²⁺ , and the Cu ²⁺ concentration can be measured from the absorption degree (height) of this wavelength. With such an optical measurement method, cuprous concentration and cupric concentration can be measured, but it is not necessary to accurately grasp cupric concentration, and specific gravity management (total liquid density) is required for its management. But it is enough. In addition, cuprous originally does not exist if ClO ₃ is excessive, and if the purpose is to control the oxidizing agent, an ORP meter or a two-electrode or three-electrode potentiostat device (constant potential electrolysis method) is used. There is no significance in introducing an optical measurement method because it may be used.
[0024]
The spectrum of sodium chlorate 1M is shown in FIG. As shown in the figure, the absorption is only at about 300 nm or less, but in this region, as shown in FIGS. 1 and 2, the absorption of the other substance is overwhelmingly large and the absorption by NaClO ₃ is hidden. There is no meaning to do. Many substances have a large absorption below 300 nm, and this absorption is not unique to sodium chlorate. Therefore, in general optical measurement, only the cuprous concentration is required, and there is no significant merit in using the optical measurement. In particular, in the excessive management method, real-time management is not achieved if the oxidizing agent is replenished when cuprous is detected (sodium chlorate is insufficient).
[0025]
-Control of hydrochloric acid concentration-As described above, when the hydrochloric acid concentration is high, chlorine dioxide and chlorine gas are generated, and when the hydrochloric acid concentration is low, the oxidation reaction is not completed. If the hydrochloric acid concentration is kept very low, a shortage of hydrochloric acid occurs immediately in the regeneration reaction, so hydrochloric acid must be replenished in real time. As means for measuring the hydrochloric acid concentration, titration analysis, conductivity, pH controller, and the like are conceivable. However, even if the titration analysis is accurate, it takes time until an analysis result is obtained, and rapid replenishment is impossible. Use of a conductivity meter is not suitable due to the very low concentration of hydrochloric acid. The reason why the conductivity meter can be used as a hydrochloric acid sensor with the cupric chloride etching solution is that the hydrochloric acid concentration is as high as 2 to 4 M, and the conductivity of hydrochloric acid is much higher than that of cupric chloride. Since the chlorate etchant is used in a state where there is almost no hydrochloric acid, the electrical conductivity measures the total amount of ions, and the measurement result is almost proportional to the specific gravity. Therefore, it is most practical to control the hydrochloric acid concentration with a pH meter, and in this case, temperature compensation is required for the measured value. In addition, the pH meter has a problem of electrode life, and in order to prevent deterioration of the comparative electrode due to contamination of the etchant, a structure with a large amount of internal liquid is required with a double junction structure.
[0026]
-Specific gravity control-Chlorate etchant can dissolve a large amount of copper due to its low hydrochloric acid concentration, and the etchant has a high specific gravity of 1.4 or more, reducing the amount of liquid in the etching tank. There are advantages. On the other hand, if the total amount of ions increases (specific gravity increases), saturation always occurs and crystals are generated. Therefore, specific gravity management is required to monitor the saturation state. The setting range of specific gravity is preferably 1.25 to 1.45.
[0027]
-Control of oxidizing agent (sodium chlorate)-In the method of replenishing the amount of oxidizing agent to oxidize Cu ⁺ produced by chlorate etchant (equivalent control method), the amount of sodium chlorate replenished is controlled by the ORP meter can do. On the other hand, in the excess liquid management method in which an oxidizer (sodium chlorate) is always present in a certain excess, there is no Cu ⁺ (reducing agent), Cu ²⁺ is an oxidizer, ClO ₃ is an oxidizer, and everything is an oxidizer. For this reason, it is impossible to control the oxidizing agent (sodium chlorate) based on the indicated value of the ORP meter, regardless of the difference in redox potential between Cu ²⁺ and ClO ₃ . Furthermore, ORP is also greatly affected by the amount of H ⁺ (pH), so it operates correctly until Cu ⁺ is oxidized, but thereafter (Cu ⁺ becomes Cu ²⁺ , and an excessive amount of oxidizing agent is added. Case) The indicated value is not reliable. Therefore, the concentration measurement of ClO ₃ in this case is only titration analysis or ion chromatography, and since the latter is difficult to use in the process, the titration method is used. Since ClO ₃ has a unique reaction with ferrous ions, this method is used for titration analysis to keep the ClO ₃ concentration constant. The range of sodium chlorate is preferably 0 to 1 mol.
[0028]
—Chlorate Etchant Management Device— FIG. 5 is a flow chart of the sodium chlorate equivalent liquid management device.
As shown in FIG. 5, this apparatus comprises a sample measuring cell (not shown) having a pH sensor, an ORP sensor, a specific gravity sensor and a temperature sensor, each connected to an amplifier, and an amplifier of each of the sensors. The control device has a CPU that receives the signal of 1 through a multiplexer and an A / D converter.
[0029]
The control device processes the input signal by the CPU and outputs a replenishment signal / alarm from the output unit according to a predetermined level of each sensor signal. For example, with respect to the pH signal, a hydrochloric acid replenishment signal is outputted so as to keep the pH at 1.3 to 1.5. In the case of equivalent liquid management, a replenishment signal for sodium chlorate regenerating liquid is output by an ORP sensor signal, and when the ORP value exceeds a certain value, a warning is output and chemical liquid replenishment is stopped. In the specific gravity sensor, when the specific gravity exceeds a certain value (1.43), a water replenishment signal is output to reduce the specific gravity. When the temperature indicated by the temperature sensor is below a certain value, the chemical solution is not replenished. If the pH and OPR sensor internal liquid is insufficient, an alarm is output.
[0030]
In the case of the sodium chlorate excess liquid management device, a titration analysis cell for controlling the sodium chlorate excess amount is provided on the measurement cell side in addition to the flow chart of FIG. In this case, the ORP sensor can be used as a detector for generating chlorine dioxide or chlorine gas.
[0031]
FIG. 6 shows a configuration in which the sodium chlorate analyzer is combined with the excess liquid management device. A potassium permanganate titrant, molle salt, and dilute sulfuric acid are introduced into the analysis cell into which the sample liquid from the etching tank is injected through a pump, and a pH sensor as other measuring means. An ORP sensor, a temperature sensor, and the like are provided in the analysis cell. The signal output of each sensor from the analysis cell is input to the CPU of the control device, and, for example, a sodium chlorate replenishment signal is output according to the result of signal processing, and an appropriate amount of oxidant is replenished to the etcher.
[0032]
When Cu ⁺ is produced by etching, detection is performed by an ORP meter, a replenishment signal is output, and sodium chlorate is added in an amount corresponding thereto. At this time, if hydrochloric acid is not added, hydrochloric acid is consumed by the regeneration reaction and the concentration decreases. If water is not added, the specific gravity increases. Then, only sodium chlorate is added until the pH reaches about 1.3 to 1.5, and water is added when the specific gravity exceeds 1.43. When the pH rises to about 1.5, the automatic supply of hydrochloric acid is started so as to maintain the pH of 1.3 to 1.5. If management is continued as it is, a sodium chlorate equivalent etching solution is obtained.
[0033]
In the case of sodium chlorate excess management, control is performed with a sodium chlorate analyzer shown in FIG. In the titration analysis method of sodium chlorate determination, a known amount of molle salt (ferrous ammonium sulfate solution) is added to a certain amount of sample injected into the analysis cell and heated for a certain period of time. Mole salt is diluted with dilute sulfuric acid to make sulfuric acid acid, and titrated with potassium permanganate standard solution for quantitative determination.
[0034]
-Comparison of etch rates-Comparison of etch rates with other etchants is shown in FIG.
In the figure:
1. Specific gravity 1.40 cupric chloride etchant (hydrochloric acid 0.5M, cupric 3.5M)
2. Cupric chloride / sodium chlorate etchant (hydrochloric acid 0.1M, cupric 3M, sodium chlorate 0.5M)
3. Specific gravity 1.25 cupric chloride etchant (conventional cupric chloride etchant)
4.38 Baume ferric chloride etchant (new solution)
[0035]
【The invention's effect】
As described above, according to the present invention, in the management of cupric chloride / sodium chlorate etching solution, the pH value, ORP meter indication value, specific gravity, and temperature of the etching solution are managed and controlled within predetermined ranges, respectively. Substantial etching that fully utilizes the characteristics of cupric / sodium chlorate-based etching solution is possible, and this control is made possible by a simple configuration device that combines a pH sensor, ORP sensor, specific gravity sensor, and temperature sensor. It can be implemented with certainty.
[Brief description of the drawings]
FIG. 1 is a spectrum diagram of a sodium chlorate etchant.
FIG. 2 is a spectrum diagram of a sodium chlorate etchant using a more powerful light source.
FIG. 3 is a spectrum diagram of a 1M sodium chlorate solution.
FIG. 4 is a comparison diagram of etch rates between etching solutions.
FIG. 5 is a flowchart of a management apparatus for a cupric chloride / sodium chlorate etching solution.
FIG. 6 is a diagram showing an outline of an excess liquid management apparatus for cupric chloride / sodium chlorate etching liquid.

Claims (3)

Cuprous chloride produced by copper etching with cupric chloride / sodium chlorate etching solution is converted to the formula: 6CuCl + NaClO ₃ + 6HCl → 6CuCl ₂ + NaCl + 3H ₂ O using sodium chlorate and hydrochloric acid. At the time of reproduction, the pH value, ORP value, sodium chlorate concentration, and specific gravity of the etching solution are measured by corresponding sensors, and the pH of the etching solution is set to 0.5 to 5 based on the signal output from the sensor. The etching solution is adjusted and managed so that the ORP value is +500 mV to +1200 mV, the sodium chlorate concentration is 0 to 1 mol, and the specific gravity is within the range of 1.25 to 1.45. Management method of cupric chloride / sodium chlorate etching solution. Cuprous chloride produced by copper etching with cupric chloride / sodium chlorate etching solution is converted to the formula: 6CuCl + NaClO ₃ + 6HCl → 6CuCl ₂ + NaCl + 3H ₂ O using sodium chlorate and hydrochloric acid. In order to regenerate, an etching solution measuring cell including a pH sensor, an ORP sensor, a specific gravity sensor and a temperature sensor, a processing unit for output signals from the sensors, and a replenishment instruction unit for generating a replenishment signal according to the processing result And a control device for the cupric chloride / sodium chlorate etching solution.   The cupric chloride / sodium chlorate-based etching solution management device according to claim 2, further comprising a titration analyzer for the concentration of the sodium chlorate.

Images